The present invention concerns an electromagnetic wave switch realized from a PIN diode mounted in a waveguide and operating for millimetric waves, especially at 94 GHz. The purpose of such a device is to transmit with a minimal loss of power the hyperfrequency signals and to attenuate to a maximum these same signals by using two polarization states.
A millimetric electromagnetic wave switch structure with PIN diode is already known, such as described in U.S. patent application Ser. No. 410,708 now U.S. Pat. No. 4,507,632 entitled "Electromagnetic wave switch". According to this patent application, the switch is constituted by a metallic ridged rectangular waveguide, for example made of copper, and of which the dimensions allow the propagation of millimetric waves, with a PIN diode made of silicon of the classic type associated to a polarization circuit and mounted in the ridged space, of a determined volume, foreseen by the guide.
Further according to this patent application, the volume of the PIN diode is identical to that of the ridged space and in a particular embodiment mentioned in the application, the dimensions of the straight section of the guide are equal to 2.54 mm by 1.27 mm, while those of the classic PIN diode are equal to b 0.6 mm in length by 0.4 mm in thickness and 0.7 mm along the longitudinal axis of the guide. This latter dimension of the PIN diode corresponds to 3.lambda..sub.g /4, i.e. a multiple of one quarter the guided wavelength .lambda..sub.g at the operating frequency of 94 GHz.
Furthermore, it is known that a classic PIN diode presents thick zones or areas P.sup.+ and N.sup.+, of about from 30 to 80 microns, this with the aim of obtaining very high breakdown voltages.
On the basis of the dimensions given above for the classic PIN diode, with respective layers P+ and N.sup.+ of 40 microns thickness, the applicant has carried out tests of this type of millimetric electromagnetic wave switches according to the prior art, at an operating frequency of 94 GHz and for a strong pulsed incident power of 1 kW.
In fact, the performances noted for this switch are poor, and in particular the insertion losses measured at low level and at zero polarization are unacceptably high, being of about 4 dB, including 3.4 dB which are due to the assembly of the PIN diode. On the other hand, the isolation, measured in direct polarization with a current value of about 20 mA, the value is of about 20 dB, which is relatively mediocre. Consequently, this classic PIN switching diode does not give satisfactory enough performances in the range of millimetric waves.